FAQ's about antibiotics in animal feed

Q: Why do livestock producers use antibiotics?

This pig has a staph infection on its ear. Antibiotics can treat this kind of infection and improve pig welfare. Photo from the Animal Science Image Gallery.Antibiotics are useful for controlling and preventing disease in livestock. Proper use can keep animals healthy, control the spread of diseases between herds, help animals gain weight and prevent the spread of diseases from animals to humans.

Q: Why are some antibiotics called "growth promotants?"

In the U.S., many livestock producers give their animals low doses of certain antibiotics to improve overall health and help animals gain weight. This is also called "subtherapeutic" use because instead of curing a specific disease, the antibiotics are used to improve overall growth and health.

Since the 1940′s, scientific studies have shown that antibiotics may improve animal growth by improving gut health. Animals play host to many kinds of gut microbes. Though many gut microbes aid in digestion and immune response, they also compete with animals for nutrients.

A 1994 study showed that as much as six percent of the net energy in the pig diet is lost to organisms in the gut. Antibiotics in animal feed can reduce this competition and help an animal gain weight more efficiently. Low doses of antibiotics can also ward off "subclinical infections" that stress the animal's immune system and slow growth.

Use of growth-promoting antibiotics is one way livestock producers meet global demand for food. In 2002, Dr. Gary Cromwell, a professor of swine nutrition at the University of Kentucky, published a paper showing that antibiotics dramatically improved pig growth. Cromwell analyzed the results of more than 1,000 growth experiments in swine over a 25-year period. In young pigs, antibiotics improved the growth rate by an average of 16.4 percent.

Q: What is antibiotic resistance?

It is widely accepted that bacteria can become resistant to antibiotics over time. In a large population of bacteria, there may be a few individuals with genes that allow them to resist antibiotics. When exposed to antibiotics, these resistant bacteria can survive while the antibiotic-susceptible individuals die off. These resistant bacteria live to pass their antibiotic-resistant genes to their offspring. Over time, more and more individuals in the population have the resistant gene. This cycle can lead to strains of antibiotic-resistant disease.

Q: Are antibiotics safe in animal feed?

On Dec. 22, 2011 the FDA reported that after 34 years of hearings on the issue, there is still no direct link between antibiotics in animals and drug-resistant human diseases.

Despite the lack of direct evidence, several organizations have spoken out against the FDA decision. Many animal scientists blame this opposition on common misconceptions about antibiotic use. According to the American Meat Science Association and the American Meat Institute, "One often-cited statistic comes from the Union of Concerned Scientists, which claims that 70 percent of antibiotics produced in the United States are fed to livestock, a statistic they cannot possibly calculate considering that antibiotic use in humans is not tracked.